JPH0239920B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a recording method for sequentially recording and reproducing television signals and audio signals on a recording medium as the same recording trajectory.

Conventional structure and its problems When recording a television signal with a video tape recorder, etc., the method shown in Figure 1 is to perform FM modulation, frequency multiplex the audio signal onto the television signal, and record it as the same recording trajectory. The luminance signal is converted into an FM modulated wave (Y-FM), the modulated color signal is frequency-converted to a low frequency C, and an FM-modulated audio signal ( A possible method is to frequency-division multiplex and record FM-A). However, when trying to record and play back such signals in a limited frequency band like a video tape recorder, FM
Inserting the audio signal may significantly limit the FM luminance signal band and modulation color signal band. In particular, when recording two-channel FM audio signals, the degree of band restriction becomes large. For example, if you use a VHS video tape recorder,
When attempting to record an FM modulated audio signal by inserting it into the intermediate frequency band between the FM luminance signal (Y-FM) and the low frequency conversion modulated color signal C, the frequency arrangement is the luminance signal band, color signal band, and audio signal S. Considering the compromise from the perspective of securing /N, the voice carrier is
Approximately 1.3MHz±50kHz is appropriate, as shown in Figure 2.

In the case of Figure 2, the lower limit of the lower sideband of the FM luminance signal is approximately 1.35MHz, which is approximately 350kHz narrower than the lower limit of approximately 1MHz of the lower sideband when there is no FM audio signal (approximately 350kHz in resolution). 30 cooling). Furthermore, when the two channels CH and CH ₂ of the FM audio signal are recorded, the frequency arrangement is approximately as shown in Figure 3.

In the case of Figure 3, the lower limit of the lower sideband of the FM luminance signal is further limited to about 200 kHz higher, to about 1.55 MHz, and the resolution is degraded by about 45 lines.
In the case of a VHS system VTR, the resolution in the NTSC system is approximately 240 lines, and multiplexing the FM audio signal degrades the resolution by approximately 30 lines (approximately 45 lines in the case of 2 channels), which leads to a significant deterioration in image quality. . It is desirable that the resolution in the NTSC system is 240 lines or more, so in order to insert and record one channel of FM modulated audio and achieve the desired image quality, the FM
It is desirable that the carrier frequency of the luminance signal be approximately 350 kHz or more higher than in the case of FIG. tentatively
If the carrier frequency of the FM brightness signal is set to a high frequency of 350 kHz, a resolution of 240 lines can be secured for one audio channel, but the resolution is 225 lines when recording two channels of audio signals.
It ends up being less than the size of a book. On the other hand, if the FM luminance signal carrier is increased by 350 kHz, the recording wavelength will be correspondingly shortened, leading to S/N deterioration of the reproduced signal. If the recording/playback device has sufficient S/N, it is possible to set it to an FM carrier that can record 2 channel audio and secure a resolution of 240 lines or more, but the recording/playback device is If there is no margin for S/N, a resolution of 240 lines is secured for one channel of audio, and for two-channel recording, the resolution is slightly sacrificed to 2.
It is conceivable to record the FM audio signal of the channel. In this case, even if the audio signal of the first channel is always recorded, the audio signal of the second channel can be recorded as needed (for example, in stereo or bilingual cases).
If the second channel is not required, the second channel's audio band can be effectively utilized as the FM brightness signal band without recording the second channel's FM audio carrier.
The presence or absence of the FM carrier in the second channel is detected, and if there is no audio FM carrier in the second channel, the lower side wave spreads to the audio band of the second channel, and the recorded FM brightness signal can be effectively reproduced. In this way, the resolution can be increased by widening the reproduced FM luminance signal band. The problem here is whether it is possible to stably identify the presence or absence of the second channel FM audio carrier in the reproduced signal.

OBJECTS OF THE INVENTION The present invention is intended to easily detect a tape on which only one channel of audio signals is recorded and a tape on which two channels of audio signals are recorded, as described above, during playback.

Structure of the Invention When recording and reproducing television signals using a video tape recorder or the like, a frequency modulated (FM) audio signal is inserted into a frequency band between a frequency modulated (FM) luminance signal and a modulated color signal that is converted to a low frequency. In a system where the FM audio signal of the first channel is always inserted and the FM audio signal of the second channel is recorded with or without insertion. During playback, the presence or absence of an FM audio carrier is detected during the vertical blanking period of the television signal, and if an FM audio carrier is detected, the playback signal processing system is activated to prevent interference from the FM audio signal from entering the playback video signal system. control fm
The aim is to make effective use of the bandwidth of the playback video signal processing system when no audio carrier is detected.

Description of Examples The brightness signal of a television signal contains signal components up to 4MHz, and the energy of each frequency component changes depending on the content of the screen, but generally it is 1MHz.
The above-mentioned high-frequency energy is small, but depending on the content of the screen, the high-frequency component may be very large.Also, in the FM modulation transmission system, the high-frequency component is preenphasized and modulated, so the high-frequency energy becomes very large. That's true. Therefore, the second channel FM is the lower sideband of the luminance FM modulated wave.
The energy coming into the audio frequency band cannot be ignored. Therefore, if you try to detect the FM audio carrier with a band pass filter (BPF) that extracts the FM audio carrier frequency of the second channel in order to detect the presence or absence of the FM audio carrier, the FM audio carrier of the second channel will not be recorded. Even in this case, the lower sideband of the FM luminance signal may enter the band of the BPF, resulting in erroneous detection. As a method to prevent this false detection, we have experimented with a method that detects the presence or absence of the second channel audio FM carrier during the vertical blanking period, which is unrelated to the image content and has little high frequency energy (lower sideband energy). It turned out to be very effective. By being able to stably detect the presence or absence of second channel audio in this way, it is no longer necessary to record an identification signal to determine whether 1 channel recording or 2 channel recording is present during recording, which is advantageous in terms of circuit configuration. is what is born.

FIG. 4 shows a block diagram of the reproduced signal processing circuit.

In FIG. 4, data is reproduced from the magnetic head 1,
The signal amplified by head amplifier 2 is passed through high-pass filter (PF) 3, low-pass filter LPF 6,
It is distributed to BPF10 and 13. The luminance FM signal (Y-FM) separated by HPF3 is ON,
FM audio signal trap circuit 4 that can be turned off
is led to the FM demodulation circuit 5 through the FM demodulation circuit 5, and the demodulated luminance signal is extracted. The low frequency modulated color signal separated by the LPF 6 is led to a color reproduction processing circuit 7, where subcarrier jitter is removed by conventional means and converted into a modulated color signal of the original standard carrier frequency. FM demodulation circuit 5
The outputs of the color reproduction processing circuit 7 and the color reproduction processing circuit 7 are added together in an adding circuit 8, and a reproduced video signal is obtained at an output terminal 9. The FM audio signal of the first channel CH ₁ separated by the BPF 10 is sent to the FM demodulation circuit 14.
A reproduced demodulated signal of CH ₁ is obtained at the output terminal 12.

The FM audio frequency band signal of the second channel CH ₂ extracted by BPF13 is FM
The signal is guided to a demodulator 14 and a gate circuit 17. On the other hand, the reproduced video signal is led to a vertical synchronizing signal separation circuit 19, and its output drives a pulse generator 20 that generates a pulse with a width within the vertical blanking period, and this pulse gates the output of the BPF 13. gated out by circuit 17;
Detector 18 detects the presence or absence of a second channel FM audio carrier. Since there is generally no video information during the vertical blanking period (VIR signals, VIT signals, and other teletext signals may enter, it may be preferable not to gate the positions where these signals enter). , the energy of the lower sideband of the FM brightness signal does not spread, and the energy of the FM audio carrier frequency band of the second channel is at an extremely low level, so the identification of the FM audio carrier of the second channel is in the lower side of the FM brightness signal. This means that it can be made stable without being affected by wave energy.
Furthermore, the section corresponding to the horizontal synchronization signal part is gated.
If it is turned OFF, the lower side wave energy of the FM luminance signal will be further reduced, and the detection margin will be further increased.

In this way, when the presence of the second channel FM audio carrier is detected, the detection signal turns on the switch circuit 15, and the demodulated audio signal of the second channel is taken out at the output terminal 16. With this, the trap circuit 4
The FM audio carrier of the second channel is removed from the FM brightness signal. It is assumed that the trap for the FM audio carrier of the first channel is always on in this case.

Figure 5 shows how to detect the presence or absence of an FM audio carrier during playback when only one channel of FM audio signal is selectively recorded.
FIG. 3 is a circuit block diagram in which the video signal band is automatically widened to obtain a wideband video signal when there is no FM audio carrier.

In FIG. 5, circuits that operate in the same way as in FIG. 4 are labeled with the same numbers. In this case, it is preferable to include a trap 4'' in the color signal circuit so that it is automatically turned on and off according to the detection signal.

Although not shown in the figure, it is clear that detection of whether two channels of FM audio signals are being recorded simultaneously or whether neither is being recorded can be realized in a similar manner.

In order to further enhance the effect of such a circuit configuration on the playback side, when an FM audio signal is recorded during recording, the video signal spectrum in the band corresponding to the FM audio band is removed and recorded.
If the FM audio signal is not recorded,
Needless to say, it is desirable to record without removing the video signal spectrum in the FM audio signal band.

Effects of the Invention According to the configuration of the present invention, when recording monaurally on a deck with 2 channel FM audio recording specifications, when selectively recording (or not recording) 1 channel FM audio signal, etc. without inputting a signal to identify the presence or absence of FM audio recording, using only the playback circuit.
It is possible to stably detect the presence or absence of an FM audio carrier, and when FM audio is not recorded, the video signal band is automatically expanded to obtain a high-resolution reproduced video signal.

[Brief explanation of drawings]

Figures 1, 2, and 3 are frequency spectrum diagrams when recording video signals and audio signals by frequency multiplexing, and Figures 4 and 5 are frequency spectrum diagrams, respectively.
Each figure is a block diagram of a reproducing system of an embodiment of a recording/reproducing apparatus according to the present invention. 1...Magnetic head, 2...Head amplifier, 3...
...High-pass filter, 4...Trap circuit, 5,1
1, 14...FM demodulation circuit, 6...Low pass filter, 7...Color reproduction processing circuit, 8...Addition circuit, 10, 13...Band filter, 15...Switch circuit, 17...Gate circuit, 18...Detector, 19...Vertical synchronization signal separation circuit, 20...Pulse generation circuit.

Claims (1)

[Claims] 1 The brightness signal of a color television signal is a frequency modulated wave, the color signal is a modulated color signal in a frequency band lower than the lower side wave band of the frequency modulated brightness signal, and the modulated color signal in the lower frequency band and the above-mentioned A recording and reproducing device configured to perform FM modulation and frequency multiplexing of two channels of audio signals in a frequency band between a frequency modulated luminance signal and record the frequency multiplexed signals on a recording medium, The first FM audio signal with low frequency components is configured to be always recorded, and the second FM audio signal with high frequency components is configured to be selectively recorded. The presence or absence of the FM audio signal carrier is detected during the vertical blanking period of the video signal, and if the second FM audio signal carrier is detected, interference due to the second FM audio signal is mixed into the reproduced video signal. 1. A recording and reproducing device for video and audio signals, characterized in that the video and audio signals are removed by a filter to prevent such signals from being generated.